Magnetic refrigeration technology at ambient temperature has been known for more than thirty years and its advantages in terms of ecology and sustainable development are widely acknowledged. Its limits in terms of its useful calorific output and its thermal performance are also well known. Consequently, all the research undertaken in this field tends to improve the performances of the magnetocaloric thermal appliances, by adjusting the various parameters, such as the intensity of the magnetic field, the performances of the magnetocaloric material, the heat exchange surface between the heat transfer fluid and the magnetocaloric materials, the performances of the heat exchangers, etc.
In these appliances, it is indispensable to generate a uniform and intense magnetic field in at least one air gap in which at least one thermal element out of magnetocaloric material enters and exits. The higher the magnetic field in the air gap, the stronger the magnetocaloric effect induced in the magnetocaloric element, which leads to an increase of the thermal output as well as of its temperature gradient and therefore of the global efficiency of such a magnetocaloric thermal appliance.
Moreover, in certain areas, the compactness of the thermal appliance is essential and leads to a rotary configuration or structure wherein the magnetic system is in relative movement with respect to the magnetocaloric material(s). Such a rotary configuration has the advantage of showing a good magnetocaloric material per used volume ratio. Since the thermal output of the thermal appliance depends in particular on the quantity of magnetocaloric material used, such arrangement is actually very advantageous.
However, there is today no magnetic field generator with a small size, a reduced cost price, that can be mounted in a rotary thermal appliance and is liable to generate an intense and uniform magnetic field concentrated to about one Tesla in at least two air gaps.